The present invention relates to wireless data communication. More particularly, the present invention relates to a novel and improved method and apparatus for power control in a wireless communication system.
In a wireless communication system, a base station communicates with multiple mobile users. The communication link from the base station to the mobile is referred to as the forward link, while the communication link from the mobile to the base station is referred to as the reverse link. In a Code Division Multiple Access (CDMA) system particularly, mobile users share a same Radio Frequency (RF) band wherein power control prevents one user from interfering with other mobiles. In one such system, power control is used to ensure sufficient quality of signals received at the base station or at the mobile. Specifically, in the reverse link, power control adjusts the transmit power of each mobile to achieve the effect that signals are centrally received by the base station at approximately the same power level. In other words, reverse link power control seeks to solve the xe2x80x9cnear-farxe2x80x9d problem in spread spectrum multiple access systems and thus increase capacity of the system. In the forward link, power control can also be employed to prevent excessive downlink transmit power interfering with the downlink transmissions in the adjacent cells. Spread spectrum systems such as CDMA systems typically employ an open loop or a closed loop power control scheme. Open loop refers to transmitter (either mobile or base station)-controlled operation where the receiver is not directly involved. For example, a particular reverse link open loop power control calls for the mobile to adjust reverse link transmit power based on the power level of signals received from the base station via the forward link. Closed loop power control expands open loop operation whereby the receiver actively participates in making the power adjustment decision. For example, for reverse link closed loop power control the base station compares the power level of signals received from a given mobile to a threshold value. The base station then instructs the mobile to increase or decrease the reverse link transmit power based on the comparison. Conversely, the mobile monitors the power level of signals received on the forward link, and provides feedback on the quality of the forward link to the base station. Closed loop operation is used to compensate for power fluctuations associated with fading, such as Raleigh fading, of a given link.
For a system in which a mobile receives multiple data streams via a common link, a problem exists in distinguishing the quality of each of the transmitted signals. There is a need therefore for an improved method of power control in a wireless communication system supporting multiple data streams via a common link. Further, there is a need for a wireless communication system supporting multiple users via a common link that considers the quality of the common link with respect to each mobile user.
The disclosed embodiments provide a novel and improved method for power control in a wireless communication system. According to one aspect, in a wireless communication system wherein multiple data streams are transmitted via a composite channel, the composite channel including a plurality of transport channels, a method for power control includes assigning a power indicator to each of the plurality of transport channels, decrementing the power indicator of each of the plurality of transport channels having a transmission error, incrementing the power indicator of each of the plurality of transport channels without a transmission error, determining a maximum power indicator from the power indicators of each of the plurality of transport channels, and making a power control decision based on the maximum power indicator.
In another aspect, a method for power control in a wireless communication system, wherein transmissions in the system use a composite transport channel having a plurality of transport channels, includes receiving data streams via the plurality of transport channels, determining an individual quality threshold for each of the plurality of transport channels, and determining a composite quality threshold for the composite transport channel, wherein the composite quality threshold is equal to a maximum of the individual quality thresholds.
In still another aspect, a wireless apparatus includes a processor operative to process multiple data streams, wherein the multiple data streams are received via a plurality of transport channels, an error detection unit coupled to the processor, the error detection unit operative to detect errors in the multiple data streams, and a power control unit adapted to calculate quality thresholds for each of a plurality of transport channels, wherein a first quality threshold associated with a first transport channel is increased on detection of an error in a first data stream transmitted via the first transport channel, wherein the power control unit is adapted to determine a power control instruction according to the quality thresholds.